Method and composition for stripping fibrous materials



Patented Apr. 11, 1939 UNITED STATES METHOD AND COMPOSITION FOR STRII PING FIBROU$ MATERIALS Hiram B. Ohannon, Portsmouth, Va., assignor to Virginia smelting Company,

Portland,

Maine, a corporation of Maine No Drawing. Application November 20, 1935, Serial No. 50,792

15 Claims.

This invention relates to a method of stripping rags and like fibrous materials, and more particularly animal fibers, such as wool waste, which may be derived from various sources and hence contain numerous dyes or other coloring materials, so as to remove such colors and leave the stock uniformly light colored or substantially white.

In the art of recovering waste materials, such as textiles or textile fibers, and more especially woolen wastes of various kinds, it is usual to find that they have been dyed in many ways and with diiferent classes of dyes. If a single dye or type of dye has been used, it may ordinarily be readily dissolved, and by selecting an appropriate stripping agent therefor, the dye will be promptly and expeditiously decolorized or removed and washed out. But different classes of dye are susceptible to different stripping agents. And conversely, a stripping agent which is effective upon one type of dye may not affect another type of dye. If materials containing two or more types of dye are present, therefore, in a mixed mass of waste materials, it would require several separate treatments in order to strip the mass, as a whole, of its color. Moreover, the successive stripping agents may conflict with one another. Again, the textile fibers present may belong in different categories, such as wool, cotton, rayon, etc., and, though usually sorted out, they may vary,at least to the extent of containing a small proportion of extraneous materials which, if not removed, would constitute a sharply contrasting colored fiber in the finished material and in the 5 products made therefrom. Such difierences in fiber material are, of course, a. fundamental reason for the use of different classes of dye in the original preparation of the goods or fiber from which the waste is derived. Thus, while mixed goods may be encountered, containing both wool and cotton, for example, with different dye components in each, it is generally true of wool alone that it may be dyed with a very wide range of dye substances and hence all-wool goods may present as wide a variation of dyes to be removed as when admixtures of cotton, rayon, etc., are present therewith.

It is, therefore, an object of the present invention to provide a method of stripping colored rags and the like which shall be competent to remove not only predominating coloring material or materials, which may be present, but also to remove smaller amounts of other dyeing or coloring materials. It is also an object to provide 5 suitable and economical stripping compositions for this purpose. It is a further object of the invention more particularly to provide for the stripping of materials derived from animal fibers such as wool or silk (as distinguished from cotton, rayon, and other vegetable fibers) in which numerous dyes may be encountered,but which will also be eifective if the materials should include some vegetable fibers. Other objects will appear from the following disclosure.

It is found, as a part of this invention, that zinc hydrosulphite tends to hydrolyze and ionize, in aqueous solutions, producing a decidedly acidic condition. This may be manifested by the development of a pH value as low as 5,'or perhaps somewhat lower, in the resulting solution.

It is now further found that zinc hydrosulphite solutions are rendered more effective as stripping agents, by lowering such acidity (or raising their pH value) so as to approximate neutrality. It is believed that such pH values are related to the natural or isoelectric values of the fibers (and more particularly of animal fibers) which are undergoing treatment. This may be done by the addition of a freely soluble alkali metal compound, (including ammonium'compounds) which is decidedly alkaline in its reactivity, such as sodium carbonate, caustic soda, sodium hydrosulphite, and the like. These compounds are characterized by neutralizing the acidic component of the zinc hydrosulphite without introducing other anions into the solution. The relative amounts of alkaline compound used may vary,with corresponding variations in the pH values of the resulting solution accordingly. If sodium hydrosulphite is used, it may be required in somewhat higher proportion to the zinc hydrosulphite. It is also found, under these conditions, that the alkali metal cations which are thus introduced into the solution by the addition of the alkaline compound are reactive with the zinc hydrosulphite, forming an effective stripping compound or reagent.

It is believed that this reaction may be represented by the equation:

But for best results in this direction it is important, if not essential, that the zinc hydrosulphite used should be freshly made from zinc dust and sulphur dioxide. While, as above indicated, the

amount of alkaline compound may be varied so as to produce a pH value of 6.0 or more, it is usually preferred that the alkali metal compound be added in approximately the proportions indicated by the equation and so that the resulting solution shall be approximately neutral or slightly alkaline as indicated by a pH value of 7.0 to 7.5. As thus prepared, it is specifically eflective in enhancing the stripping action of the solution toward various waste dyed materials, both in kind and in degree. That is to say, the stripping action of the reagent solution is rendered more energetic and also is found to be capable of removing a wider range of dye substances which may be contained in the goods to be stripped than the usual hydrosulphite solutions as previously employed.

Since the range of dyes which may be'employed in dyeing wool or animal fibers is extensive and hence the number of dyeing materials in any given lot of goods under treatment may be large, this is an extremely important advantage. Certain inert vat dyes or pigment colors are un affected but, with these few exceptions, practically all of the usual dyes, including vegetable tanning extracts, which are difficult to attack, may be decolorized and/or removed.

It follows, therefore, that by thus modifying and controlling the composition and condition of the zinc hydrosulphite solution, a mixture of animal fibers, such as waste wool fibers, fabrics, and the like, may be given a single stripping treatment for the removal of its coloring matters, and the various dyes will be rendered soluble and removed or decolorized; so that the resulting product will present a uniformly depleted color value, or be substantially white, and there will be practically no colored impurities or fibers left in the mass.

In a typical instance of the practical application of the invention, for example, waste woolen rags or wool fiber, may be first washed with a caustic alkali solution, such as ammonium or sodium hydroxide, with agitation and boiling. The charge is then drained and preferably washed free of dissolved matter from the wool and free of the reagents used.

A solution of zinc hydrosulphite is prepared, preferably in a fresh lot for the purpose,-as by introducing liquid sulphur dioxide into a water suspension of zinc dust, in the proportions of 2 lbs. S02, 1 lb. zinc dust, and 1 gallon of water. When the reaction is complete, as indicated by the nearly complete solution of zinc dust, the solution is treated with approximately one-half an equivalent of sodium hydroxide,- e. 40/65 lb. NaOH.

The alkaline pre-treated fiber, washed, and carried in a suitable suspension of water, is now charged into a rotary boiler (unless the preliminary alkaline treatment has been effected therein which may be convenient )and the freshly prepared hydrosulphite solution added in sufficient amount to wet the charge thoroughly and permit working and handling. The boiler and its contents are then preferably agitated, as by rota-' tion, and heated to approximately F. and held at such temperature for about 30 to 60 minutes.

The amount of reagent used will vary somewhat, dependent upon the materials to be treated, etc., but approximately 8% to 15% of hydrosulphite on the weight of the charge of wool undergoing treatment is found to be sufficient in most cases.

The charge is then promptly removed, drained, and washed free from entrained solids and liquids, with fresh water, and finally dried. It will be found to be uniformly decolorized or stripped, and hence ready for substantially any of the purposes which well stripped or decolorized waste materials are adapted to serve.

If the waste material, which is to be stripped, is fairly clean, it may be advantageous simply to drain the stock, after its preliminary treatment with the alkaline solution, and to utilize the residual alkali which is retained by the fibers. partially to neutralize the subsequently added zinc hydrosulphite solution. In such cases, however, it will be necessary to ascertain the amount of caustic which is thus held by the goods, in order to avoid adding an excess. In this way, an economy of caustic soda or other alkaline compound used may be effected. To this end, it may also be found desirable to conduct the preliminary alkaline treatment in two stepsremoving the first lot of alkaline solution substantially completely, and washing, if desired,-

drained off may be used to treat the next subsequent batch of waste material while the portion entrained with the fibers serves partially to neutralize the zinc hydrosulphite which is subsequently applied to this batch of fibrous material in its further course of treatment.

It is to be understood, also, that while the preliminary alkaline treatment of the waste material (or other materials to be stripped or decolorized) is usually desirable, it is not necessary to the process of the invention and that the goods may also be effectively stripped by the hydrosulphite treatment, as above described, alone.

It should be understood that the present disclosure is for the purpose of illustration only and that this invention includes all modifications and equivalents which fall within the scope of the appended claims..

I claim:

1. Method of stripping dye from waste fibrous materials, composed largely of animal fibers such as wool, which comprises the steps of treating the same with an alkaline solution, washing, and thereafter treating with a solution of zinc hydrosulphite to which has been added approximately one-half the chemical equivalent of an alkaline compound of an alkali metal.

2. Method of stripping dye from waste fibrous materials, composed largely of animal fibers such as wool, which comprises the steps of treating the same with an alkaline solution, washing and thereafter treating with a solution of zinc hydrosulphite to which has been added approximately one-half the chemical equivalent of an alkali metal hydroxide.

3. Method of stripping dye from waste fibrous materials, composed largely of animal fibers such as wool, which comprises the steps of treating the same with an alkaline solution, washing, and thereafter treating with a solution of zinc hydrosulphite which has been substantially neutralized with sodium hydroxide.

4. Method of stripping dye from waste fibrous materials, composed largely of animal fibers such as wool, which comprises the step of treating the materials, composed largely of animal fibers such as wool, which comprises the step of adding an alkaline solution, removing the same, treating with a second alkaline solution, and thereafter treating with a solution of zinc hydrosulphite, under substantially neutral conditions.

6. A dye stripping solution for waste fibrous materials, composed largely of animal fibers such as wool, characterized by containing the reaction product of a freshly prepared solution of zinc hydrosulphite and an alkaline compound of an alkali metal and by having a pH value of approximately 6.0 to 7.5.

7. A dye stripping solution for waste fibrous materials, composed largely of animal fibers such as wool, characterized by containing the reaction product of a freshly prepared solution of zinc hydrosulphite and an alkaline sodium compound and by being substantially neutral.

8. A dye stripping solution for waste fibrous materials, composed largely of animal fibers such as wool, characterized .by containing the reaction product of a freshly prepared solution of zinc hydrosulphite and approximately one-half an equivalent of an alkaline compound of an alkali metal and by being substantially neutral.

9. A dye stripping solution for waste fibrous materials, composed largely of animal fibers such as wool, characterized by containing the reaction product of zinc hydrosulphite and approximately one-half an equivalent of an alkali metal hydroxide and by being substantially neutral.

10. A dye stripping solution for waste fibrous materials, composed largely of animal fibers such as wool, characterized by containing the reaction product of zinc hydrosulphite and approximately one-half an equivalent of sodium hydroxide.

11. A dye stripping solution for waste fibrous materials, composed largely of animal fibers such as wool, characterized by consisting of a solution of freshly prepared zinc hydrosulphite plus an alkaline compound of an alkali metal which is substantially neutral.

12. Method of preparing dye stripping reagents comprising the step of reacting a solution of zinc hydrosulphite with approximately onehaii' equivalent of an alkali metal compound. thereby to render the same substantially neutral.

13. Method of preparing dye stripping reagents comprising the step of reacting a solution of zinc hydrosulphite with approximately onehalf equivalent of an alkali metal hydroxide, thereby to render the same substantially neutral.

14. Method of preparing dye stripping reagents comprising the step of reacting a solution of zinc hydrosulphite with approximately onehalf equivalent of an alkaline sodium compound, thereby to render the same substantially neutral.

15. Method of preparing dye stripping reagents comprising the step of reacting a solution of zinc hydrosulphite with approximately onehaif equivalent of sodium hydroxide.

' HIRAM B. CHANNON. 

